Is that the only difference between the two databases?
There are a lot of thing that can impact the performance. Like the number of indexes, number of rows already in the table, I/O bandwidth, tablespace type, and on and on.
First compare all the dbm and db config parameters and see what is different. you can also read this article and see if it can help:
http://www.ibm.com/developerworks/db...m-0403wilkins/
Andy